---
title: Use Bun
description: A guide on using Bun with Expo and EAS.
---

import { Terminal } from '~/ui/components/Snippet';

[Bun](https://bun.sh/) is a JavaScript runtime and a drop-in alternative for [Node.js](https://nodejs.org/en). In Expo projects, Bun can be used to install npm packages and run Node.js scripts. The benefits of using Bun are faster package installation than npm, pnpm, or yarn and [at least 4x faster startup time compared to Node.js](https://bun.sh/docs#design-goals), which gives a huge boost to your local development experience.

## Prerequisites

To create a new app using Bun, [install Bun on your local machine](https://bun.sh/docs/installation#installing).

## Start a new Expo project with Bun

To create a new project, run the command:

<Terminal cmd={['$ bun create expo my-app']} />

You can also run any **package.json** script with `bun run`:

<Terminal cmd={['$ bun run ios']} />

To install any Expo library, you can use `bun expo install`:

<Terminal cmd={['$ bun expo install expo-av']} />

## Use Bun for EAS builds

EAS decides which package manager to use based on the lockfile in your codebase. If you want EAS to use Bun, run `bun install` in your codebase which will create a **bun.lockb** (the Bun lockfile). As long as this lockfile is in your codebase, Bun will be used as the package manager for your builds. Make sure to delete any lockfiles generated by other package managers.

### Customize Bun version on EAS

Bun is installed by default when using EAS. See the [Android server images](/build-reference/infrastructure/#android-server-images) and [iOS server images](/build-reference/infrastructure/#ios-server-images) to learn which version of Bun is used by your build's image.

To use an [exact version of Bun](/eas/json/#bun) with EAS, add the version number in **eas.json** under the build profile's configuration. For example, the configuration below specifies Bun version `1.0.0` for the `development` build profile:

{/* prettier-ignore */}
```json eas.json
{
  "build": {
    "development": {
      /* @info Use <CODE>bun</CODE> property in eas.json to specify the exact version.*/
      "bun": "1.0.0"
      /* @end */
      /* @hide ... */ /* @end */
    }
    /* @hide ... */ /* @end */
  }
}
```

## Migrate to using Bun from npm, pnpm or yarn

It is currently not possible to import another package manager's lockfile into Bun (though this feature is being [worked on](https://github.com/oven-sh/bun/issues/1751)). Until this is done, there is an element of risk to switching over to Bun on an existing project.

The purpose of a lockfile is to _lock_ down your dependency tree. If there is a library in **package.json** whose version number starts with a `^` or `~`, you are likely to end up with a different version of the package.

- `^` means you're opting into future minor and patch versions
- `~` means you're opting into future patch versions only

According to Semantic Versioning (SemVer), minor and patch versions do not include breaking changes. Unfortunately, breaking changes can still slip through. Since a lockdown file contains **specific versions** of dependencies, you will not get updates unless you explicitly opt-in. By deleting the lockfile, you are losing that safety and getting the latest versions available of all the packages as defined in your **package.json**.

To migrate to using Bun (use at your own risk):

<Terminal
  cmd={[
    '$ rm -rf node_modules',
    '$ rm yarn.lock pnpm-lock.yaml package-lock.json',
    '$ bun install',
  ]}
/>

## Trusted dependencies

Unlike other package managers, Bun does not automatically execute lifecycle scripts from installed libraries, as this is considered a security risk. However, if a package you are installing has a `postinstall` script that you want to run, you have to explicitly state that by including that library in your [`trustedDependencies`](https://bun.sh/guides/install/trusted) array in your **package.json**.

For example, if you install `packageA`, which has a dependency on `packageB` and `packageB` has a `postinstall` script, you must add `packageB` in your `trustedDependencies`.

To add a trusted dependency in your **package.json**, add:

```json package.json
"trustedDependencies": ["your-dependency"]
```

Then, remove your lockfile and re-install the dependencies:

<Terminal cmd={['$ rm -rf node_modules', '$ rm bun.lockb', '$ bun install']} />

## Common errors

### EAS Build fails when using Sentry and Bun

If you're using `sentry-expo` or `@sentry/react-native`, these depend on `@sentry/cli`, which updates source maps to Sentry during your build. The `@sentry/cli` package has a `postinstall` script which needs to run for the "upload source maps" script to become available.

To fix this, add `@sentry/cli` to your [trusted dependencies](/#trusted-dependencies) array in **package.json**:

```json package.json
"trustedDependencies": ["@sentry/cli"]
```
